Testing, testing...

[JASmith]

True, but the situation continues to evolve. The widespread distribution of 7.62mm rifles and MGs down to section level (helped by the fact that the British have just joined the US in selecting the 7.62mm Minimi) has to a large degree addressed the range and (to some extent) the effectiveness issues of 5.56mm, but has created a new problem - ammo weight!

The plastic case technology you called our attention will make a huge difference and, and one could forecast, reduce the pressure to replace the 7.62X51 machine gun in the heavy dismounted role.

...We may be able to get away with being close enough to M80 performance for the difference not to be significant, rather than exactly matching it. However, if the long-range performance falls noticeably short then the new round won't be able to replace 7.62mm and the argument for it will thereby be substantially weakened IMO...

We (especially me) keep forgetting that we live in a combined arms world. There was a recent (History, History International, or Discover Channel - I don't remember which) segment on the Barret rifle development, history and future plans. They appear to have implemented a variant of their M-107 that uses the 25 mm grenades developed, IIRC, for the now defunct OICM family of weapons.

True -- a 16-20 lb weapon and even heavier ammunition may be challenging to lug around, but the developments are there and will affect the 1 km game. These developments show possibilities. E. g., I remember seeing discussions on the web (~5 years ago) featuring an experimental UK guided 12 gauge round.

While a guided 12 gauge round, for the time being, would almost certainly be horrifically expensive, an unguided variant could be developed today and use existing under-barrel mounts for many of the weapons already in service. Further, the payload could be combined effects, shrapnel plus a shaped charge. The shaped charge would likely be able to pierce 20-30 mm of armor plate, making it capable of defeating the most effective forecast body armor. This, coupled with sights like the Barrett BORS, could give the squad-level sharpshooter some very interesting teeth.

Bottom line -- I see these other developments as factors we can't or should not ignore.

When we factor that sort of thing into the assessment and are willing to accept one ammunition type (e. g. 85-90 gr 6.5) for box magazines and another (e. g. 115 to 130 gr 6.5 mm) for belted, while still maintaining the potential for interchangeability in emergencies, then a "one caliber" dismounted infantry solution appears feasible.